Gas Turbine Rotor Blade Radial Thickness Variation
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Solution Overview
Problem
Gas turbine engine rotor blades experience vibrations, particularly chordwise bending stresses, due to thinner tip areas, leading to tip cracking, performance losses, and reduced lifespan, with existing solutions either compromising aerodynamic performance or inducing radial loading by increasing thickness or reducing chord length.
Innovation Solution
The rotor blade design features a radial span-dependent chord length and maximum thickness to chord length ratio (Tmax/C ratio) that varies across the blade, with a root portion, tip portion, and mid portion, each with distinct Tmax/C ratios, distributing vibratory stresses across a larger area while maintaining aerodynamic performance and minimizing natural frequency changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the blade thickness is increased to reduce tip vibrations, then vibratory stresses are reduced, but aerodynamic performance deteriorates and radial loading increases
Solution Approach 1:
The patent applies local quality by varying the maximum thickness to chord length ratio (Tmax/C) at different radial spans of the blade. The root portion has a first Tmax/C ratio, the tip portion has a second Tmax/C ratio, and the mid portion has a third Tmax/C ratio that is less than both the first and second ratios. This localized variation allows the blade to have sufficient thickness at the tip to reduce vibratory stresses while maintaining thinner mid-sections that preserve aerodynamic performance and minimize radial loading.
2Strength
If the chord length is reduced to reduce tip vibrations, then vibratory stresses are reduced, but aerodynamic performance deteriorates
Solution Approach 1:
The patent uses local quality by implementing radial span-dependent chord length C and maximum thickness T with varying Tmax/C ratios. The tip portion has a higher Tmax/C ratio than the mid portion, allowing the tip to have adequate thickness for vibration resistance while the overall chord length remains optimized for aerodynamic performance. This localized thickness variation resolves the contradiction between vibration resistance and aerodynamic efficiency.
3Strength
If the blade thickness is increased uniformly, then tip vibrations are reduced, but radial loading into the rotor assembly increases
Solution Approach 1:
The patent applies local quality by creating a non-uniform thickness distribution along the radial span. The mid portion has a lower Tmax/C ratio compared to the tip and root portions. This localized thinning in the mid-section reduces the overall mass and radial loading on the rotor assembly, while the thicker tip portion (with higher Tmax/C ratio) provides sufficient stiffness to reduce tip vibrations and distribute stresses effectively.
Data Source
AI summary
Methods and apparatus for fabricating a rotor blade for a gas turbine engine are provided. The rotor blade includes an airfoil having a first sidewall and a second sidewall, connected at a leading edge and at a trailing edge. The method includes forming the airfoil portion bounded by a root portion at a zero percent radial span and a tip portion at a one hundred percent radial span, the airfoil having a radial span dependent chord length C, a respective maximum thickness T, and a maximum thickness to chord length ratio (Tmax/C ratio), forming the root portion having a first Tmax/C ratio, forming the tip portion having a second Tmax/C ratio, and forming a mid portion extending between a first radial span and a second radial span having a third Tmax/C ratio, the third Tmax/C ratio being less than the first Tmax/C ratio and the second Tmax/C ratio.